The proposed work is concerned with examining the role of vagal afferent activity from pulmonary mechanoreceptors in control of neural output to the diaphragm and other inspiratory muscles. The studies both relate to the normal physiological role of these receptors, and how their transduction and reflex effects are disturbed in intrinsic lung disease. Particular attention is given to the recently described positive feedback loop, by which increases in lung inflation cause an increase in inspiratory neural output by a vagal reflex. Studies are directed at characterizing this feedback loop, investigating its physiological function, and determining how the function of this loop is disturbed in certain common lung diseases. The particular receptors, which might mediate this loop, are being studied. Quantitative techniques are being developed and applied to characterize the responses of both pulmonary rapidly-adapting and stretch receptors to dynamic lung inflations.